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Context.— Studies of lungs in patients with COVID-19 have focused on early findings. Objective.— To systematically study histopathologic and imaging features and presence of SARS-CoV-2 RNA in lung tissue from patients in later stages of COVID-19. Design.— Autopsies, explants, surgical lung biopsies, transbronchial biopsies, cryobiopsies, and needle biopsies from patients with COVID-19 whose onset of symptoms/confirmed diagnosis was more than 28 days before the procedure were studied. Available images were reviewed. Reverse transcription droplet digital polymerase chain reaction for SARS-CoV-2 RNA was performed on lung tissue. Results.— Of 44 specimens (43 patients; median age, 59.3 years; 26 [60.5%] male) features of acute lung injury (ALI) were seen in 39 (88.6%), predominantly organizing pneumonia and diffuse alveolar damage, up to 298 days after onset of COVID-19. Fibrotic changes were found in 33 specimens (75%), most commonly fibrotic diffuse alveolar damage (n = 22) and cicatricial organizing pneumonia (n = 12). Time between acquiring COVID-19 and specimen was shorter in patients with diffuse ALI (median, 61.5 days) compared with patients with focal (140 days) or no ALI (130 days) (P = .009). Sixteen (of 20; 80%) SARS-CoV-2 reverse transcription droplet digital polymerase chain reaction tests were positive, up to 174 days after COVID-19 onset. Time between COVID-19 onset and most recent computed tomography in patients with consolidation on imaging was shorter (median, 43.0 days) versus in patients without consolidation (87.5 days; P = .02). Reticulations were associated with longer time to computed tomography after COVID-19 onset (median, 82 versus 23.5 days; P = .006). Conclusions.— ALI and SARS-CoV-2 RNA can be detected in patients with COVID-19 for many months. ALI may evolve into fibrotic interstitial lung disease.

Supplementary Figure 1 from Atypical Protein Kinase Cι Is Required for Bronchioalveolar Stem Cell Expansion and Lung Tumorigenesis

The use of lymphoid interstitial pneumonia (LIP) as a diagnostic term has changed considerably since its introduction. Utilizing a multi-institutional collection of 201 cases from the last 20 years that demonstrate features associated with the LIP rubric, we compared cases meeting strict histologic criteria of LIP per American Thoracic Society (ATS)/European Respiratory Society (ERS) consensus ("pathologic LIP"; n=62) with cystic cases fulfilling radiologic ATS/ERS criteria ("radiologic LIP"; n=33) and with other diffuse benign lymphoid proliferations. "Pathologic LIP" was associated with immune dysregulation including autoimmune disorders and immune deficiency, whereas "radiologic LIP" was only seen with autoimmune disorders. No case of idiopathic LIP was found. On histology, "pathologic LIP" represented a subgroup of 70% (62/88) of cases with the distinctive pattern of diffuse expansile lymphoid infiltrates. In contrast, "radiologic LIP" demonstrated a broad spectrum of inflammatory patterns, airway-centered inflammation being most common (52%; 17/33). Only 5 cases with radiologic cysts also met consensus ATS/ERS criteria for "pathologic LIP." Overall, broad overlap was observed with the remaining study cases that failed to meet consensus criteria for "radiologic LIP" and/or "pathologic LIP." These data raise concerns about the practical use of the term LIP as currently defined. What radiologists and pathologist encounter as LIP differs remarkably, but neither "radiologic LIP" nor "pathologic LIP" present with sufficiently distinct findings to delineate such cases from other patterns of diffuse benign lymphoid proliferations. As a result of this study, we believe LIP should be abandoned as a pathologic and radiologic diagnosis.

Small cell lung carcinoma (SCLC) is characterized by high metastatic rate and poor prognosis. The platinum-based chemotherapy still represents the backbone of the therapy; however, acquired resistance develops almost in all patients. Although SCLC has been formerly considered a homogeneous disease, recent advances in SCLC research have highlighted the importance of inter- and intratumoral heterogeneity and have resulted in the subclassification of SCLC. The newly described SCLC subtypes are characterized by distinct biological behavior and vulnerabilities that can be therapeutically exploited. The PI3K/Akt/mTOR pathway is frequently affected in SCLC, and its activation represents a promising therapeutic target. Since the mTOR pathway is a master regulator of cellular metabolism, its alterations may also influence the bioenergetic processes of SCLC cells. Despite the encouraging preclinical results, both mTOR and metabolic inhibitors have met limited clinical success so far. Patient selection for personalized therapy, the development of rational drug combinations, and a better understanding of heterogeneity and spatiotemporal evolution of the tumor cells may improve efficacy and can help to overcome acquired resistance. Here we provide a summary of current investigations regarding the role of the mTOR pathway and metabolic alterations in the progression and metastasis formation of SCLC.

Localized malignant mesotheliomas (LMM) is an uncommon and poorly recognized neoplasm. Its pathologic diagnosis is often surprising in patients with serosal/subserosal based localized tumors that are clinically suspicious for metastatic lesions or primary sarcomas. Once a tumor is diagnosed as "mesothelioma", LMM is often mistaken for diffuse malignant mesothelioma (DMM). Best currently available evidence about LMM was collected from the literature and cases diagnosed by members of the International Mesothelioma Panel (IMP). One hundred and one (101) LMM have been reported in the English literature. Patients had localized tumors with identical histopathologic features to DMM. Patients ranged in age from 6 to 82 years; 75% were men. Most (82%) of the tumors were intrathoracic. Others presented as intrahepatic, mesenteric, gastric, pancreatic, umbilical, splenic, and abdominal wall lesions. Tumors varied in size from 0.6 to 15 cm. Most patients underwent surgical resection and/or chemotherapy or radiation therapy. Median survival in a subset of patients was 29 months. Seventy two additional LMM from IMP institutions ranged in age from 28 to 95 years; 58.3% were men. Sixty tumors (83.3%) were intrathoracic, others presented in intraabdominal sites. Tumors varied in size from 1.2 to 19 cm. Median survival for 51 cases was 134 months. Best evidence was used to formulate guidelines for the diagnosis of LMM. It is important to distinguish LMM from DMM as their treatment and prognosis is different. A multidisciplinary approach is needed for the diagnosis of LMM as it shows identical histopathology and immunophenotype to DMM.

Case Presentation A 64-year-old man presented for consideration for lung transplant. He had a history of previous tobacco use, OSA on CPAP therapy, and gastroesophageal reflux disease. He worked as a design engineer. The patient had a 4-year history of dyspnea on exertion, followed with periodic CT scan of the chest. Nine months prior to his evaluation for lung transplant, the patient developed worsening of dyspnea, dry cough, poor appetite, and weight loss. At times, the cough was violent and associated with chest pressure. He was prescribed systemic corticosteroids and antibiotics without improvement. Four months later, the patient noted sudden onset of severe chest pain and worsening dyspnea. A CT scan of the chest demonstrated extensive pneumomediastinum in addition to changes consistent with pulmonary fibrosis. An esophagogram showed thickening of the distal esophagus, but no signs of perforation. He was prescribed supplemental oxygen and advised to stop the use of CPAP. The patient sought a second opinion. A CT scan of the chest showed improvement of the pneumomediastinum and extensive fibrotic lung disease. Pulmonary function tests (PFTs) were consistent with a restrictive pattern, decreased diffusing capacity (Dlco), and a preserved residual volume over total lung capacity ratio. The patient was prescribed systemic corticosteroids with no improvement of his symptoms. Repeat PFTs showed further decline of Dlco, and he was referred for lung transplant evaluation.

Substantial changes in the 2021 WHO Classification of Tumors of the Pleura and Pericardium since the 2015 WHO Classification include the following: (1) pleural and pericardial tumors have been combined in one chapter whereas in the 2015 WHO, pericardial tumors were classified with cardiac tumors; (2) well-differentiated papillary mesothelioma has been renamed well-differentiated papillary mesothelial tumor given growing evidence that these tumors exhibit relatively indolent behavior; (3) localized and diffuse mesothelioma no longer include the term "malignant" as a prefix; (4) mesothelioma in situ has been added to the 2021 classification because these lesions can now be recognized by loss of BAP1 and/or MTAP by immunohistochemistry and/or CDKN2A homozygous deletion by fluorescence in situ hybridization; (5) the three main histologic subtypes (i.e., epithelioid, biphasic, and sarcomatoid) remain the same but architectural patterns and cytologic and stromal features are more formally incorporated into the 2021 classification on the basis of their prognostic significance; (6) nuclear grading for epithelioid diffuse mesothelioma is introduced, and it is recommended to record this and other histologically prognostic features in pathology reports; (7) BAP1, EZH2, and MTAP immunohistochemistry have been found to be useful in separating benign mesothelial proliferations from mesothelioma; (8) biphasic mesothelioma can be diagnosed in small biopsies having both epithelioid and sarcomatoid components even if the amount of one component is less than 10%; and (9) the most frequently altered genes in diffuse pleural mesothelioma include BAP1, CDKN2A, NF2, TP53, SETD2, and SETDB1.

Small cell lung carcinoma (SCLC) accounts for approximately 15% of all lung cancers and remains a challenging disease, with no significant improvement in the field of targeted therapies. The RICTOR gene (rapamycin-insensitive companion of mTOR [mammalian target of rapamycin]), which encodes a key structural (scaffold) protein of mTOR complex 2), has recently been identified as one of the most frequently amplified genes and a potential therapeutic target in SCLC. The aim of this study was to compare immunohistochemical (IHC) expression of Rictor and phospho-Akt (a downstream target of mTOR complex 2) with RICTOR amplification as detected by fluorescence in situ hybridization (FISH) in SCLC. RICTOR FISH and Rictor and phospho-Akt IHC staining were performed on 100 formalin-fixed, paraffin-embedded SCLC samples. RICTOR amplification was detected in 15 samples (15%). IHC positivity for Rictor and phospho-Akt was observed in 37 (37%) and 42 (42%) samples, respectively. Considering FISH as the diagnostic standard, the sensitivity and specificity of Rictor IHC were 93% and 73%, whereas the sensitivity and specificity of phospho-Akt IHC were 80% and 65%, respectively. Rictor expression was higher in distant metastases than in primary tumor samples and lymph node metastases. There was no association between RICTOR amplification and clinical outcome. However, high expression of either Rictor or phospho-Akt was associated with significantly decreased overall survival. In conclusion, IHC expression of Rictor correlates highly with RICTOR amplification. Therefore, Rictor IHC can be used as a cost-effective method to select patients for RICTOR FISH and, potentially, for mTORC1/2 inhibitor therapy.

Endobronchial tumors (ET) are unusual and mostly malignant, presenting with non-specific symptoms that often delay appropriate diagnosis and treatment. Lymphomas in the airway represent less than 1% of pulmonary malignancies and require multidisciplinary approach for their management. We present a case of a 48-year-old male former smoker with a one-year history of recurrent respiratory infections and new-onset shortness of breath. Diagnostic tests included a chest computed tomography (CT) reporting the presence of an endobronchial mass and neck and cervical lymph node biopsies with inconclusive results. Bronchoscopy was successfully performed for tumor resection, improving the patient’s respiratory symptoms. Histological analysis described an extranodal marginal zone B-cell lymphoma (ENMZL) with plasmacytic differentiation; a subtype of non-Hodgkin’s lymphoma (NHL) in mucosa-associated lymphoid tissue (MALT), rarely found as an endobronchial growth. ET should be considered in the setting of persistent and worsening respiratory symptoms. ENMZL with plasmacytic differentiation is rarely found as an ET and diagnosis requires bronchoscopic intervention and extensive immunohistochemical analysis.

Thymoma and paraganglioma are known causes of mediastinal masses, the latter being extremely rare. Thymomas arise from remnant thymic tissue in the anterior mediastinum; whereas, thoracic paragangliomas arise from para-aortic or para-vertebral sympathetic chain ganglion (derivatives of embryonic neural crest) in the middle or posterior mediastinum. We report a case of a middle-aged woman with two mediastinal masses, originally believed to be a single tumor or primary malignancy with adjacent metastasis on Computed Tomography (CT) that were further delineated with Magnetic Resonance Imaging (MRI) and [68Ga]-DOTA-(Tyr3)-octreotate (DOTA-TATE) Positron Emission Tomography-Computed Tomography (PET-CT) and surgical pathology as two distinct entities: left epicardial paraganglioma and anterior mediastinal thymoma. A comprehensive discussion of both entities is included.

mTOR activation has been observed in rhabdomyosarcoma (RMS), however, mTOR complex (mTORC) 1 inhibition has had limited success thus far. mTOR activation alters the metabolic pathways, which is linked to survival and metastasis. These pathways have not been thoroughly analyzed in RMSs. We performed immunohistochemistry on 65 samples to analyze the expression of mTOR complexes (pmTOR, pS6, Rictor), and several metabolic enzymes (phosphofructokinase, lactate dehydrogenase-A, &beta, F1-ATPase, glucose-6-phosphate dehydrogenase, glutaminase). RICTOR amplification, as a potential mechanism of Rictor overexpression, was analyzed by FISH and digital droplet PCR. In total, 64% of the studied primary samples showed mTOR activity with an mTORC2 dominance (82%). Chemotherapy did not cause any relevant change in mTOR activity. Elevated mTOR activity was associated with a worse prognosis in relapsed cases. RICTOR amplification was not confirmed in any of the cases. Our findings suggest the importance of the Warburg effect and the pentose-phosphate pathway beside a glutamine demand in RMS cells. The expression pattern of the studied mTOR markers can explain the inefficacy of mTORC1 inhibitor therapy. Therefore, we suggest performing a detailed investigation of the mTOR profile before administering mTORC1 inhibitor therapy. Furthermore, our findings highlight that targeting the metabolic plasticity could be an alternative therapeutic approach.

Summary: Lung squamous cell carcinoma (LSCC) is a prevalent form of lung cancer exhibiting distinctive histological and genetic characteristics. Chromosome 3q26 copy number gain (CNG) is a genetic hallmark of LSCC present in >90% of tumors. We report that 3q26 CNGs occur early in LSCC tumorigenesis, persist during tumor progression, and drive coordinate overexpression of PRKCI, SOX2, and ECT2. Overexpression of PRKCI, SOX2, and ECT2 in the context of Trp53 loss is sufficient to transform mouse lung basal stem cells into tumors with histological and genomic features of LSCC. Functionally, PRKCI and SOX2 collaborate to activate an extensive transcriptional program that enforces a lineage-restricted LSCC phenotype, whereas PRKCI and ECT2 collaborate to promote oncogenic growth. Gene signatures indicative of PKCι-SOX2 and PKCι-ECT2 signaling activity are enriched in the classical subtype of human LSCC and predict distinct therapeutic vulnerabilities. Thus, the PRKCI, SOX2, and ECT2 oncogenes represent a multigenic driver of LSCC. : Liu et al. report that three oncogenes, PRKCI, SOX2, and ECT2, which are coordinately amplified and overexpressed in lung squamous cell carcinoma (LSCC), can transform Trp53−/− mouse lung basal stem cells into tumors with histological and genomic features of LSCC and drive oncogenic signaling necessary to maintain a LSCC phenotype. Keywords: lung squamous cell carcinoma, LSCC, 3q26 copy number gain, CNG, PRKCI, SOX2, ECT2, lung basal stem cells, oncogenic transformation

COPA syndrome is a newly discovered, rare genetic autoimmune disorder, which can affect the lungs, joints, and kidneys. It is difficult to recognize, and the survival benefit of lung transplantation for these patients is not yet known. We present a case of a 24-year-old woman who received bilateral lung transplant for COPA syndrome. At 15 months posttransplant, her pulmonary function is stable with no episodes of acute cellular- or antibody-mediated rejection and no evidence of disease recurrence.

With the discovery of rapamycin 45 years ago, studies in the mechanistic target of rapamycin (mTOR) field started 2 decades before the identification of the mTOR kinase. Over the years, studies revealed that the mTOR signaling is a master regulator of homeostasis and integrates a variety of environmental signals to regulate cell growth, proliferation, and metabolism. Deregulation of mTOR signaling, particularly hyperactivation, frequently occurs in human tumors. Recent advances in molecular profiling have identified mutations or amplification of certain genes coding proteins involved in the mTOR pathway (eg, PIK3CA, PTEN, STK11, and RICTOR) as the most common reasons contributing to mTOR hyperactivation. These genetic alterations of the mTOR pathway are frequently observed in lung neoplasms and may serve as a target for personalized therapy. mTOR inhibitor monotherapy has met limited clinical success so far; however, rational drug combinations are promising to improve efficacy and overcome acquired resistance. A better understanding of mTOR signaling may have the potential to help translation of mTOR pathway inhibitors into the clinical setting.

Pathology of Vaping-Associated Lung Injury This letter describes findings in 17 patients with a history of vaping who had lung biopsies after presenting with symptoms and bilateral pulmonary opacit...

Background Patients with ANCA-positive vasculitis may develop interstitial lung disease (ILD), it is an uncommon but increasingly recognised manifestation. Clinical characteristics and prognosis are not well known in these patients. The largest report to date is from East Asia describing microscopic polyangitis (MPA) as the most common association with ILD. Objectives To describe the cliniccal manifestatiions and response to therapy of patients with AAV and ILd compared with patients with idiopathic pulmonary fibrosis (IPF) and interstitial pneumonia with autoimmune features (IPAF) Methods We conducted a retrospective 10 year chart review at the Mayo Clinic Florida, including patients with confirmed diagnoses of both AAV and ILD done by expert rheumatology and pulmonology clinical evaluations. Clinical characteristics of ANCA-ILD in 24 patients were compared to 29 patients with idiopathic pulmonary fibrosis (IPF) and 22 patients with interstitial pneumonia with autoimmune features (IPAF), which were confirmed by applying the IPF diagnostic criteria based on the most recent ATS guidelines and IPAF criteria defined by Fischer and colleagues, respectively. Results We identified 24 ANCA-ILD patients. 14 patients had MPA, 12 patients had granulomatosis with polyangitis (GPA), and 2 patients had eosinophilic granulomatosis with polyangitis (EGPA). 54% were female and mean age was 70. In half of the ANCA-ILD patients, vasculitis presented prior to ILD, mainly MPA, 36% of patients presented with ILD first, most of them with GPA. The rest presented with ILD and vasculitis at the same time. Usual interstitial pneumonia (UIP) was the most common radiographic pattern. Honeycombing was more common in MPA compared to GPA patients. Ground glass opacity was present in 5 (63%) of GPA and in 5 (36%) of MPA patients. Most MPA patients had positive anti-MPO antibody and p-ANCA. Only one GPA patient had positive anti-MPO antibody and two were p-ANCA positive. The majority of the GPA patients were positive for anti-proteinase-3 antibody and c-ANCA. The mainstay of treatment was corticosteroids. Rituximab was used in 14 patients. The decline in functional vital capacity (FVC) and diffusing capacity (DLCO) was most marked in IPF group, followed by ANCA-ILD and then the IPAF group (Δ FVC, −0.5,–0.5, and 0.3 L/s; Δ DLCO, −3.7,–3.6, and −0.1, respectively). In a similar manner, survival was poorest in IPF, followed by ANCA-ILD and was best in the IPAF group. Conclusions This is, to our knowledge, the largest case series of clinically confirmed AAV with ILD in North America. Sizable number of GPA with c-ANCA positive patients presenting concomitant ILD is a novel observation for the clinical characteristics of ANCA-ILD that contradicts previous epidemiology of ANCA-ILD. Our data is also of value by adding prognostic information in an era of newer therapeutics, such as rituximab. In addition, the intermediate prognosis of ANCA-ILD, between IPF and IPAF, is very interesting especially after the new classification IPAF. Disclosure of Interest None declared

Lymphangioleiomyomatosis (LAM) is a rare progressive cystic lung disease with features of a low-grade neoplasm. It is primarily caused by mutations in TSC1 or TSC2 genes. Sirolimus, an inhibitor of mTOR complex 1 (mTORC1), slows down disease progression in some, but not all patients. Hitherto, other potential therapeutic targets such as mTOR complex 2 (mTORC2) and various metabolic pathways have not been investigated in human LAM tissues. The aim of this study was to assess activities of mTORC1, mTORC2 and various metabolic pathways in human LAM tissues through analysis of protein expression. Immunohistochemical analysis of p-S6 (mTORC1 downstream protein), Rictor (mTORC2 scaffold protein) as well as GLUT1, GAPDH, ATPB, GLS, MCT1, ACSS2 and CPT1A (metabolic pathway markers) were performed on lung tissue from 11 patients with sporadic LAM. Immunoreactivity was assessed in LAM cells with bronchial smooth muscle cells as controls. Expression of p-S6, Rictor, GAPDH, GLS, MCT1, ACSS2 and CPT1A was significantly higher in LAM cells than in bronchial smooth muscle cells (P

Lung transplantation may offer longer survival and improved quality of life to patients with end-stage lung disease. Common indications for single lung transplantation include chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis­, and α 1 -antitrypsin deficiency emphysema. Bilateral lung transplantation is the norm for cystic fibrosis, but the proportion of bilateral (double) lung transplantation procedures has been rising for other major indications as well. Benchmark survival rates for adult lung transplant recipients are 89% at 3 months, 80% at 1 year, 65% at 3 years, 54% at 5 years, and 31% at 10 years after transplantation. Complications of lung transplantation may be related to (1) the operation itself (primary graft dysfunction, anastomotic complications), (2) the host’s immunologic response to the allograft (rejection), and (3) the immunosuppressive therapy used to prevent rejection (infection, posttransplantation lymphoproliferative disorder [PTLD]). Other complications, such as organizing pneumonia and recurrence of the original disease, may also occur. Posttransplantation transbronchial biopsy may be performed for a specific clinical indication or for surveillance of acute rejection. The histopathologic findings most commonly encountered in a posttransplantation transbronchial biopsy include acute rejection, cytomegalovirus infection, airway-centered inflammation, pneumonia, bronchiolitis obliterans, harvest injury, invasive aspergillosis, and PTLD.

Pleomorphic lobular carcinoma (PLC), a variant of invasive lobular carcinoma (ILC) is described as an aggressive tumor with poor prognosis. Multiple studies show lower overall survival for patients with PLC than for patients with classic ILC (cILC). We compared the clinicopathologic characteristics of PLC with those of cILC. All cases with a diagnosis of ILC, Nottingham grades 2 or 3 that were diagnosed between January 1, 1990, and December 31, 2010, were retrieved from pathology files in the institutional anatomic pathology database. The cases (N = 52) were reviewed to identify those meeting the criteria for PLC. An E-cadherin immunostain was used to confirm the lobular immunophenotype. Clinicopathologic data were assessed and analyzed. A control group (N = 103) of cILC, Nottingham grade 1, was selected, with 2 controls for each case, matched by age and year of diagnosis. PLC was associated more closely with in situ carcinoma (P = .03), and had lower progesterone receptor expression (P = .03) than cILC. Both disease-free survival and overall survival were similar between patients with PLC and matched cILC controls, and both depended on disease stage, tumor size, and lymph node status. PLC is similar to cILC in terms of patient survival and outcomes.

A 51-year-old man was admitted for evaluation of new-onset generalized seizures in the context of progressive and significant behavioral change. His medical history was only notable for previous outbreaks of genital herpes. He took no medications. He had occasional social alcohol use and no illicit drug use but was a 35-pack-year current smoker. The patient had no relevant occupational exposure history but had recently traveled to Panama. Initially, the patient's significant other noticed a progressive flattening of his affect. The patient then started to experience episodes of "passing out" that led to injuries prompting ED visits. He was prescribed antiseizure medications and scheduled for an outpatient workup. However, with progressive gait instability, lethargy, and an increase in frequency of generalized seizures, the patient was admitted for treatment of suspected viral encephalitis. Despite initiation of antimicrobial and antiviral therapy, the patient's level of alertness continued to decline, ultimately leading to intubation for airway protection.

Hypersensitivity pneumonitis (HP) is a lung disease that develops in susceptible individuals after inhalational exposure to an organic antigen or chemical compound. Pathogenesis is attributed to a combination of type III (immune complex-mediated) and type IV (delayed) hypersensitivity reactions to the inciting agent.- To provide an overview of the current status of the medical literature regarding hypersensitivity pneumonitis.- A literature search was performed using PubMed and Google search engines. The terms "hypersensitivity pneumonitis" and "extrinsic allergic alveolitis" were used, with the search starting on January 9, 2017, and concluding March 8, 2017.- As a pathologist, it is important to consider hypersensitivity pneumonitis when examining lung specimens because it is often clinically and pathologically overlooked. Recognizing the often subtle findings and correlating them with the patient's history or suggesting a thorough clinical investigation of potential exposures can be of help in identifying the underlying condition so that the patient can be appropriately managed.

Immunohistochemistry is used to distinguish sarcomatoid malignant mesotheliomas (SMM) from spindle cell and pleomorphic carcinomas (SPC) but there are no guidelines on how to interpret cases that show overlapping or equivocal immunohistochemical findings. A systematic literature review of the immunophenotype of these lesions was performed and the experience with 587 SMM and 46 SPC at MESOPATH was collected. Data were analyzed with Comprehensive Meta-Analysis 2.0 software (Biostat, Englewood, NJ). There were insufficient data to evaluate the differential diagnosis between SPC and localized SMM or peritoneal SMM. Meta-analysis showed considerable overlap in the immunophenotype of these neoplasms and significant data heterogeneity amongst many of the results. Survival data from MESOPATH patients showed no significant differences in overall survival between SMM and SPC patients. Best available evidence was used to formulate several evidence-based guidelines for the differential diagnosis between pleural SMM and SPC. These guidelines emphasize the need to correlate the histopathological findings with clinical and imaging information. Diffuse SMM can be diagnosed with certainty in the presence of malignant spindle cell pleural lesions showing immunoreactivity for cytokeratin and mesothelial markers and negative staining for epithelial markers. Criteria for the interpretation of various other combinations of immunoreactivity for cytokeratin and mesothelial and/or epithelial markers are proposed. Localized sarcomatoid mesotheliomas can only be diagnosed in the presence of spindle cell malignancies that exhibit immunoreactivity for cytokeratin and mesothelial markers and negative immunoreactivity for epithelial lesions, in patients that show no multifocal or diffuse pleural spread and no evidence for extrapleural lesions.

Context.—Amyloidosis is a heterogeneous group of diseases characterized by the deposition of congophilic amyloid fibrils in the extracellular matrix of tissues and organs. To date, 31 fibril proteins have been identified in humans, and it is now recommended that amyloidoses be named after these fibril proteins. Based on this classification scheme, the most common forms of amyloidosis include systemic AL (formerly primary), systemic AA (formerly secondary), systemic wild-type ATTR (formerly age-related or senile systemic), and systemic hereditary ATTR amyloidosis (formerly familial amyloid polyneuropathy). Three different clinicopathologic forms of amyloidosis can be seen in the lungs: diffuse alveolar-septal amyloidosis, nodular pulmonary amyloidosis, and tracheobronchial amyloidosis.Objective.—To clarify the relationship between the fibril protein–based amyloidosis classification system and the clinicopathologic forms of pulmonary amyloidosis and to provide a useful guide for diagnosing these entities for the practicing pathologist.Data Sources.—This is a narrative review based on PubMed searches and the authors' own experiences.Conclusions.—Diffuse alveolar-septal amyloidosis is usually caused by systemic AL amyloidosis, whereas nodular pulmonary amyloidosis and tracheobronchial amyloidosis usually represent localized AL amyloidosis. However, these generalized scenarios cannot always be applied to individual cases. Because the treatment options for amyloidosis are dependent on the fibril protein–based classifications and whether the process is systemic or localized, the workup of new clinically relevant cases should include amyloid subtyping (preferably with mass spectrometry–based proteomic analysis) and further clinical investigation.

A 40-year-old woman (a nonsmoker) with history of idiopathic thrombocytopenic purpura and a platelet count > 90,000 cells/μL without specific medication was referred to pulmonary clinic for evaluation of multiple pulmonary nodules. The patient presented to an outside hospital with fatigue, lack of energy, and dyspnea on exertion for 2 years. She denied fever, cough, chest pain, or weight loss. An initial chest radiograph showed bilateral multiple pulmonary nodules. A chest CT scan revealed multiple nodular lesions, varying in size, in all lobes of both lungs. There was no mediastinal lymphadenopathy or pleural effusion. There was no significant hypermetabolic activity on a subsequent fluorodeoxyglucose PET scan/CT scan, and there had been no significant change. She underwent CT scan-guided percutaneous transthoracic biopsy and bronchoscopy with transbronchial biopsies, all of which were inconclusive. An open lung biopsy was considered.

A 60-year-old woman was referred to the pulmonary clinic for evaluation of lung nodules. Her medical history was notable for hypothyroidism, anxiety, and a ruptured breast implant for which incomplete surgical resection and evacuation had been performed 10 years previously. She was a lifelong nonsmoker and worked as a gym instructor. The patient denied occupational exposures and had not traveled recently. Medications included levothyroxine and alprazolam. Except for a 1-month history of occasional dry cough, the review of systems was negative. The patient's physician queried whether the previously ruptured silicone breast implant may have played a role in the genesis of the nodules and referred the patient to our institution for further management. The lack of systemic symptoms relative to the degree of lung involvement provided an early diagnostic clue.

Summary We report that mouse LSL-KrasG12D;Trp53fl/fl (KP)-mediated lung adenocarcinoma (LADC) tumorigenesis can proceed through both PKCι-dependent and PKCι-independent pathways. The predominant pathway involves PKCι-dependent transformation of bronchoalveolar stem cells (BASCs). However, KP mice harboring conditional knock out Prkci alleles (KPI mice) develop LADC tumors through PKCι-independent transformation of Axin2+ alveolar type 2 (AT2) stem cells. Transformed growth of KPI, but not KP, tumors is blocked by Wnt pathway inhibition in vitro and in vivo. Furthermore, a KPI-derived genomic signature predicts sensitivity of human LADC cells to Wnt inhibition, and identifies a distinct subset of primary LADC tumors exhibiting a KPI-like genotype. Thus, LADC can develop through both PKCι-dependent and PKCι-independent pathways, resulting in tumors exhibiting distinct oncogenic signaling and pharmacologic vulnerabilities.